Consider the set S defined recursively as follows:
• 3 ∈ S,
• if x,y ∈ S,then x−y∈S,
• if x∈S, then 2x ∈ S,
• S contains no other element.
Use Structural Induction to write a detailed, carefully structured proof that
∀ x ∈ S, ∃ n ∈ Z, x = 3n.
What I've got is since 3 is in the set...